I'm assuming that Rengifo can’t be optioned, but he’s certainly not bulletproof from a DFA.
Perkins, Ortiz, and Mitchell all certainly can, and all should be on notice. Frelick isn’t untouchable. I am not sure about Hamilton.
There are moves the Brewers can make that still preserve roster flexibility. Pratt coming up for Ortiz couldn’t be easier, procedurally. Bringing up Jett and/or Lara requires a 40 man roster spot, but they can create one anytime by moving Zerpa to the 60.